A hall effect sensor can be configured with a biasing magnet and used to detect the presence or absence of a tooth on a gear wheel. Such sensors are often used to determine the position of the CAM and crankshafts in a modem gasoline or diesel internal combustion engine. The performance requirements demanded of such a sensor in automotive applications are dictated by the timing accuracy and repeatability needed to ensure that the emissions generated by the engine meet the legislated requirements.
A further requirement for automotive applications is that of determining the position of the gear wheel, tooth or gap, almost instantaneously upon power on, known as True Power On (TPO). Such a requirement demands measurement accuracy sufficient to differentiate tooth from gap without any opportunity for the system to learn anything about the circumstances under which it is operating.
To achieve the accuracy necessary for the TPO determination demands special techniques. One such technique uses chopper amplifiers, which introduce phase delays incompatible with the demands of timing necessary to achieve the mechanical positional accuracy demanded. Current real time techniques lack the accuracy required for TPO determinations.
Accordingly it is desirable to provide a sensor arrangement that meets the demands of TPO determinations, mechanical positional accuracy and repeatability.
The present invention provides a novel sensor system including a switching arrangement that meets the needs of TPO determinations, mechanical positional accuracy and repeatability and also compensates for temperature and long term drift. The switching arrangement according to the present invention configures the elements of a hall effect sensor for operation in various modes. A first mode is optimized for determining the presence or absence of a gear tooth at start up and a second mode is optimized for timing accuracy. Additional circuitry is provided for measuring, computing and storing values for error signals and thresholds.
The sensor system of the present invention includes magnetic sensing elements and circuitry configured to detect the presence or absence of an article, such as a gear tooth, in a first mode, and to determine timing accuracy in a second mode. Control circuitry is provided for controlling the switching circuitry to switch between modes in a predetermined manner and at predetermined times dependent upon the voltages and magnetic fields. The magnetic sensing elements as well as the switching circuitry, interface circuitry and the control circuitry are preferably integrated onto a single silicon chip to yield an efficient and reliable sensor system. Upon power on, the sensor is configured in the first mode to determine the presence or absence of the article next to the sensor. After a number of transitions of the hall voltage, e.g., indicating a predetermined number of gear teeth have passed the sensor, the sensor is switched to the second mode, and the sensor operates in a dynamic time continuous manner to determine speed and timing parameters.
According to the present invention, a sensor system is provided which typically includes a hall plate and first switching circuitry for connecting supply and measurement nodes to pairs of diagonally opposite nodes of the hall plate. The sensor also typically includes a chopper amplifier whose input is connected to the measurement nodes, a clock system for controlling the timing of the switching circuitry and the timing of the chopper amplifier, and a comparator that determines the level of the chopper amplifier output relative to a reference voltage and sets a digital output to a first level when the value of the output voltage is greater than a first threshold value and to a second level when the output voltage is less than a second threshold value. Additionally, the sensor elements of the present invention typically interoperate such that the hall plate is used in a switched arrangement synchronized with the chopper amplifier, the hall voltages from the two orthogonal measurements are averaged to produce the chopper amplifier output, and the hall voltages from the two orthogonal measurements are subtracted one from the other to determine a value for the error signal.
The sensor also typically includes switching circuitry that selectively connects and disconnects the components in a number of configurations, and control circuitry that configures the sensor in a first mode when the power is first applied to the sensor, and to a second dynamic mode after an initial measurement is made in the first mode. After a predefined period, the control circuitry switches the sensor to a second mode wherein the hall plate is held in a steady condition. In the second mode, the hall plate is driven across one pair of opposite connections, the measurement points connected to the other pair of opposite connections, and the hall plate measurement points are connected to a steady state amplifier whose output is connected to a comparator circuit. The comparator circuit thresholds are derived from a calculation of the maximum and minimum hall voltages averaged over a time period added to the determined value of the error signal in such a manner as to counter the effects of the error signal on the accuracy of the timing of the switching of the comparator relative to the mechanical movement of the sensed article.
According to an aspect of the invention, a magnetic sensor system is provided that typically comprises a hall plate having two pairs of connection nodes, a power supply for providing power to the hall plate, and a switching circuit configured to alternately couple one pair of the connection nodes to the power supply and the other pair of connection nodes to measurement nodes. The system also typically comprises a first amplifier circuit, a second amplifier circuit, and a mode switching circuit coupled to the switching circuit and configured to control the switching circuit to connect the measurement nodes of the first amplifier to the hall plate in a first mode, and to connect the measurement nodes of the second amplifier to the hall plate in a second mode. In operation, in the first mode, the mode switching circuit controls the switching circuit to connect the pairs of connection nodes to the power supply and the measurement nodes of the first amplifier circuit in an alternating manner, and in the second mode, the mode switching circuit controls the switching circuit to connect one of the pairs of connection nodes to the power supply and the other pair to the measurement nodes of the second amplifier circuit.
According to another aspect of the invention, a magnetic sensor system is provided, which typically comprises a magnetic sensing means for detecting magnetic fields, the magnetic sensing means having two pairs of connection nodes, power supply means for providing power to the magnetic sensing means, and switching means for alternately coupling one pair of the connection nodes to the power supply and the other pair of connection nodes to measurement nodes. The system also typically includes first and second amplifier circuits that provide first and second voltage signals, respectively, a first comparator means for comparing the first voltage signal received from the first amplifier circuit with a first reference voltage, and a second comparator means for comparing the second voltage signal received from the second amplifier circuit with a second reference voltage and a third reference voltage. The system also typically includes a mode switching means, coupled to the switching means, for controlling the switching means to connect the measurement nodes of the first amplifier to the magnetic sensing means in a first mode, and to connect the measurement nodes of the second amplifier to the magnetic sensing means in a second mode. In operation, in the first mode, the mode switching means controls the switching means to connect the pairs of connection nodes to the power supply means and the measurement nodes of the first amplifier circuit in an alternating manner, wherein the first comparator means provides a first signal if the first voltage signal is above a first threshold value and a second signal if the first voltage signal is below the first threshold value. In the second mode, the mode switching means controls the switching means to connect one of the pairs of connection nodes to the power supply and the other pair to the measurement nodes of the second amplifier circuit in a steady state, wherein the second comparator means provides a third signal if the second voltage signal exceeds a second threshold value and a fourth signal if the second voltage signal falls below a third threshold value.
According to yet another aspect of the present invention, a method is provided for determining position and timing parameters of gear teeth on a gear wheel using an integrated sensor device located proximal the gear wheel. The method typically comprises the steps of detecting the presence or absence of a gear tooth proximal the device in a first mode of operation, and thereafter determining timing parameters of the gear wheel in a second mode of operation. The step of detecting typically includes connecting, in an alternating manner, measurement nodes of a first amplifier to one pair of connection nodes of a hall plate and the other pair of connection nodes to a power supply using a switching circuit so as to produce a first voltage signal, providing the first voltage signal from the first amplifier to a first comparator, comparing, using the first comparator, the first voltage signal with a first reference voltage, and providing an indication signal from the first comparator, wherein the indication signal is set to one of a first value if the first voltage signal is greater than the reference voltage and a second value if the first voltage signal is less than the reference voltage. The step of determining timing parameters typically includes connecting, in a continuous manner, measurement nodes of a second amplifier to one pair of connection nodes and the other pair of connection nodes to the power supply using the switching circuit so as to produce a second voltage signal, providing the second voltage signal from the second amplifier to a second comparator, comparing, using the second comparator, the second voltage signal with second and third reference voltages, and providing a second indication signal from the second comparator, wherein the second indication signal is set to one of a first value if the second voltage signal rises above the second reference voltage and a second value if the second voltage signal falls below the third reference voltage.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.